Epoxy resin compositions each containing an epoxy resin and a curing agent therefor as essential components are excellent in physical properties such as heat resistance, moisture resistance, etc., and are thus widely used for electronic components such as a semiconductor encapsulating material, a printed circuit board, and the like, the electronic component field, conductive adhesives such as conductive paste, and the like, other adhesives, matrixes for composite materials, coating materials, photoresist materials, color developing materials, etc.
Among these applications, semiconductor devices for converting a direct current to an alternating current and for finely controlling current flows and voltage rise and fall have recently attracted particular attention, and are called “power semiconductor”, “power device”, or “power module”. The power semiconductors provide a technique essential for increasing power efficiency and energy saving, and applications such as motor control for automotive cars, power control for solar power generation, wind power generation, and the like extend from day to day.
A problem of such power semiconductors lies in how to dissipate with high efficiency the large heat generated, and a rate-determining factor of heat dissipation efficiency lies in a thermal interface material (TIM) for the purpose of decreasing contact thermal resistance between a semiconductor portion and a heat sink.
TIM is mainly composed of an inorganic filler and a matrix resin, and silicone-based thermally conductive grease has been used as the matrix resin of TIM. However, required levels of performances such as thermal conductivity, resistance to thermal decomposition, adhesion to substrates, etc. are increased more and more with increases in density of semiconductor devices and amounts of electric power to be controlled, and thus it is becoming difficult for usual silicone-based heat-conductive grease to comply with this problem.
The characteristics required for TIM are roughly divided into two: (1) efficient heat transfer from a heating element to a heat-dissipating member, and (2) flexible following of thermal deformation of the heating element and heat-dissipating member. Many usual epoxy resins have been developed with importance placed on heat resistance, and have unsatisfactory thermal conductivity and low flexibility because they have relatively rigid skeletons. On the other hand, polymer materials having good flexibility produce large phonon scattering and thus have low thermal conductivity, and thus development of highly thermally conductive epoxy resins optimum for TIM has been expected.
For example, an epoxy resin represented by general formula (3) or general formula (4) below has been proposed as a resin material having excellent thermal conductivity when composited with an inorganic filler (refer to Patent Literature 1 below).

(In the formulae, X represents a single bond, a —CH═CH— group, a —COO— group, a —CONH— group, or a —CO— group, Y represents a hydrogen atom or a methyl group, p represents a number of 0 to 6, and q represents a number of 1 to 18.)
The epoxy resin has excellent thermal conductivity as compared with usual epoxy resins, but has thermal conductivity at an unsatisfactory level and poor adhesion to substrates.